Cold storage units such as freezers and dewars are used for various purposes, including the storage of biological samples over short and long periods of time. For example, biological materials for transplantation such as blood, tissue, or plasma may require storage for short periods of time before use. In another example, biological cells such as DNA samples may be stored for longer periods of time. Conventional cold storage units may be cooled by mechanical refrigeration circuits or by other methods, including the provision of liquid nitrogen (“LN2”). One type of cold storage unit used to store biological samples is known as an “ultra-low temperature freezer” (“ULT”), which is used to cool its inner storage chamber to relatively low temperatures such as about −80° C. or lower, for example.
Known cold storage units are configured to contain a plurality of storage boxes supported on different types of storage racks within a cooled cabinet. One type of storage rack referred to as a side access storage rack is configured to contain a rectangular array of storage boxes and provide access to these storage boxes through an open front side of the storage rack. To this end, this type of side access storage rack includes a housing with a top wall and a bottom wall connected at the ends by first and second end walls. The top and bottom walls are formed from one piece of sheet material connected by a rear side wall that extends between the top wall and the bottom wall. The first and second end walls may also be formed from the same piece of sheet material and bent into position such that the first and second end walls are spot welded to the top and bottom walls.
A plurality of vertical dividers extend from the rear side wall and are aligned in a series between the first and second end walls. Similarly, a plurality of horizontal shelves are inserted into engagement with the first and second end walls and with the plurality of vertical dividers, thereby splitting the space within the storage rack into a grid of box receptacles, with each box receptacle being sized to receive a storage box therein. The side access storage rack defines an open front side through which the storage boxes on the plurality of horizontal shelves may be retrieved from and returned to the storage rack.
A horizontal shelf 300 used with the conventional side access storage rack described above is shown in FIG. 8. The shelf 300 includes a planar shelf surface 302 and a pair of connection tabs 304 bent upwardly from the shelf surface 302 at opposed ends thereof. The shelf surface 302 includes a plurality of shelf slots 306 configured to receive corresponding vertical dividers when the shelf 300 is inserted into the housing of the side access storage rack. The connection tabs 304 include snap connection notches 308 that are configured to snap into engagement with corresponding projecting tabs (not shown) extending inwardly from the first and second end walls of the housing. In one example, these projecting tabs are formed in a separate end plate which is spot welded to each of the first and second end walls, thereby increasing the number of parts needed to form the side access storage rack. These snap connection notches 308 and the corresponding projecting tabs must also be specially machined from the corresponding elements of the storage rack before assembly.
This additional machining adds manufacturing time and expense to the overall assembly of the side access storage rack. When the projecting tabs are formed in separate end plates connected to the first and second end walls, the end plates add additional weight and materials cost to the side access storage rack. Furthermore, correctly snapping the shelves 300 into position requires additional assembly time. Once the side access storage rack is assembled, the horizontal shelves 300 are held primarily by the plurality of projecting tabs, which are designed with some resiliency to snap into engagement with the snap connection notches 308. Consequently, the horizontal shelves 300 are prone to small vibrations resulting at least in part from this resiliency and also in part from the long lengths between support points when the side access storage rack is moved. Even though the horizontal shelves 300 are securely held within the housing, the vibrations may provide the undesirable impression that the side access storage rack is unstable or poorly assembled.
There is a need, therefore, for a side access storage rack for use with a cold storage unit that improves the manufacturing process while providing improved performance compared to conventional side access storage racks.